Radio systems of L1 and LOK series of
spacecraft

Sven Grahn

Deductions from external features of L1 Zond spacecraft

Zond and Soyuz share the
same basic design, but there are differences between the craft. The differences
in outward appearance between Soyuz and Zond that relate to radio systems can be
summarized as follows:

The Zond had no orbital
module, but instead a small inverted conical unit equipped with:

a dish antenna with a
diameter of 1.2 meters for the main downlink on 922.76 MHz and possibly also
for receiving commands on 768 MHz. On 922 MHz the beamwidth of this dish is
about 20 degrees. The earth subtends an angle of 1.7 degrees when viewed fom
the moon.

two small antennas on
ground planes. These small antennas
look like cylinders with about 5 cm diameter and 5
cm height and may contain a a half-wave loop. The may be omni antennas intended
for 922.76 MHz.

There are two devices that
look like a large handle on each side of the Zond equipment module. The length
of the "handle" is about 1.0 meter. If this dimension represents half a
wavelength then this antenna could be intended for the 102 MHz uplink and
183.6 MHz downlink of the old Soviet deep space TT&C system.

Whip antennas on the Zond
solar panel tips are about half the length of those on the Soyuz and mounted
on the rear edge of the panel instead of on the front edge. These whips are
each about 2.0 meters long. If they have the same electrical length as those
on Soyuz then they are a quarter wavelength long, i.e. cut for a wavelength of
8 meters, i.e. about 38 MHz. If the whips are cut for half a wavelength, then
the frequency is 76 MHz.

The two spacecraft are
similar in that there is a ring of dipoles around the base of the descent
module. This antenna is the command reception antenna for 768
MHz.

Information from other
sources

Very
little information used to be available in the public domain about frequencies
used by the Zond system. In the past only informal information was available to
support the assumption that a 922.76 MHz downlink was used. However, a recent
Russian publication (1) provides
plenty of detail of the radio system. This source indicates that the basic
Saturn-MS ground stations were also used for early Soyuz and Salyut missions and
gives the uplink as "770 MHz" and the downlink as "920 MHz", which confirms
the early guesses as to frequency. The sketch below from (1) (my
translations of the captions) shows the various signalling modes on
this basic link. Interestingly, the command-verication signals have been
heard from early Soyuz, Progress and Salyut craft around 925.24-925.25 MHz,
which is indeed 2.5 MHz from the center frequency, just as indicated below.
Listen to the command-verification signal from Soyuz-34 in June 1979 here
.

Informal hints from
personal acquaintancies mention 183 MHz as a downlink.
The analysis of the pictures of Zond seem to support the use of the
old 183/102 MHz TT&C systems as a back-up.

However, the whip antennas on
the solar panel tips are difficult to tie to a specific downlink frequency. It
is difficult to envisage that 76-80 MHz was used in deep space, since the "Tral"
telemetry system that used this frequency range was a wideband system operating
in low earth orbit. It seems more reasonable to assume that the whips were used
for a frequency near 40 MHz, perhaps the same type of simple telemetry that was
transmitted by the early Luna probes on 39.986 MHz.

Summary

It seems reasonable to conclude
that the main telemetry, command and tracking link used by Zond 4-8 was the
922.76 MHz downlink with the uplink at 768 MHz. In addition a back-up system
using omni antennas seems to have operated on the old Soviet deep space TT&C
system that used 183.6 MHz as a downlink and 102 MHz as an uplink. Perhaps 40
MHz was used for very low rate housekeeping telemetry.

L3 radio systems

According to (1) the LOK vehicle used the same
frequencies as L1, i.e. 922/768 MHz and also a VHF uplink. Here is a
translation of a sentence from Molotov's book:

"... The meter-band (106 MHz) was used
for a "request signal" in a noncoherent channel, while the working frequency
of the reply channel was shifted by 6.5 MHz with respect to
the frequency of the coherent channel ..."

By "the
coherent channel" Molotov probably means 922 MHz. In all probability this
non-coherent uplink on 106 MHz was a back-up command link. It is not easy to
find an antenna for this frequency on sketches of LOK. Perhaps the little rod in
the picture below is this antenna. In other sketches there appears to be at least
two such antennas.